Manufacturability analysis for non-feature-based objects

This dissertation presents a general methodology for evaluating key manufacturability indicators using an approach that does not require feature recognition, or feature-based design input. The contributions involve methods for computing three manufacturability indicators that can be applied in a hierarchical manner. The analysis begins with the computation of visibility, which determines the potential manufacturability of a part using material removal processes such as CNC machining. This manufacturability indicator is purely based on accessibility, without considering the actual machine setup and tooling. Then, the analysis becomes more specific by analyzing the complexity in setup planning for the part; i.e. how the part geometry can be oriented to a cutting tool in an accessible manner. This indicator establishes if the part geometry is accessible about an axis of rotation, namely, whether it can be manufactured on a 4th-axis indexed machining system. The third indicator is geometric machinability, which is computed for each machining operation to indicate the actual manufacturability when employing a cutting tool with specific shape and size. The three manufacturability indicators presented in this dissertation are usable as steps in a process; however they can be executed alone or hierarchically in order to render manufacturability information. At the end of this dissertation, a Multi-Layered Visibility Map is proposed, which would serve as a re-design mechanism that can guide a part design toward increased manufacturability

Computer aided process planning for multi-axis CNC machining using feature free polygonal CAD models

This dissertation provides new methods for the general area of Computer Aided Process Planning, often referred to as CAPP. It specifically focuses on 3 challenging problems in the area of multi-axis CNC machining process using feature free polygonal CAD models. The first research problem involves a new method for the rapid machining of Multi-Surface Parts. These types of parts typically have different requirements for each surface, for example, surface finish, accuracy, or functionality. The CAPP algorithms developed for this problem ensure the complete rapid machining of multi surface parts by providing better setup orientations to machine each surface. The second research problem is related to a new method for discrete multi-axis CNC machining of part models using feature free polygonal CAD models. This problem specifically considers a generic 3-axis CNC machining process for which CAPP algorithms are developed. These algorithms allow the rapid machining of a wide variety of parts with higher geometric accuracy by enabling access to visible surfaces through the choice of appropriate machine tool configurations (i.e. number of axes). The third research problem addresses challenges with geometric singularities that can occur when 2D slice models are used in process planning. The conversion from CAD to slice model results in the loss of model surface information, the consequence of which could be suboptimal or incorrect process planning. The algorithms developed here facilitate transfer of complete surface geometry information from CAD to slice models. The work of this dissertation will aid in developing the next generation of CAPP tools and result in lower cost and more accurately machined components

STEP based Finish Machining CAPP system

This research paper presents various methodologies developed in a STEP based Computer Aided Process Planning (CAPP) system named "Finish Machining – CAPP" (FM-CAPP). It is developed to generate automatic process plans for finish machining prismatic parts. It is designed in a modular fashion consisting of three main modules, namely (i) Feature Recognition module (FRM) (ii) Machining Planning Module (MPM) and (iii) Setup Planning Module (SPM). The FRM Module analyses the geometrical and topological information of the inputted part in STEP AP 203/AP214 formats, and generates a text file with full dimensional details of features and machinable volumes. It is then passed on to the MPM for the selection of best suited machining process. Here, the selection is based on a 7 stage elimination strategy considering major manufacturing factors. After machining planning, the task of selecting the best suited setup is implemented in the SPM module. When these tasks are completed, the system generates the process-planning sheet containing the details of feature, finish cut machinable volume, machining processes with the cutting tool/ media, process parameters and the setup required for machining

Glass-Ceramics for Non-Metallic Dental Implant Applications

Metallic dental implants are an important treatment for the replacement of missing teeth. However, for esthetic and environmental issues, there is a need to develop non-metallic dental implant materials. In this thesis, two novel glass-ceramics (GCs), miserite and wollastonite, were synthesized for one-piece dental implant applications. Glasses were synthesized by wet chemical methods, followed by calcination, melting and quenching. The crystallization kinetics of these glasses were determined by differential thermal analysis (DTA). GC specimens were produced by cold pressing of the glass powder and sintering using schedules determined by DTA. The crystalline phases and microstructure of the GC samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. Miserite GC displayed an interlocking lath-like crystalline morphology. Mechanical testing results showed Dynamic Young’s modulus (E), 96±3 GPa, true hardness (Ho), 5.27±0.26 GPa, fracture toughness (KIC), 4.77±0.27 MPa∙m0.5, and brittleness index (BI), 1.11±0.05 µm-0.5, indicating suitable mechanical properties and machinability. Miserite GC showed excellent bioactivity, with formation of a hydroxyapatite surface layer when soaked in simulated body fluid (SBF). Osteoblast-like cells exhibited attachment, spreading and proliferation on miserite GC surfaces, demonstrating biocompatibility. However, preliminary studies revealed that the chemical stability of miserite GC was not optimal, prompting us to modify the GC composition. Accordingly, wollastonite GC was synthesized; it consisted of dense acicular interlocking crystals and demonstrated excellent machinability. E, Ho and KIC were 90±3 GPa, 5.15±0.47 GPa and 4.91±0.26 MPa∙m0.5, respectively. Importantly, chemical durability of wollastonite GC satisfied ISO 6872 specification for dental ceramics. Furthermore, when evaluated according to ISO 10993-14, there was little chemical degradation. In addition, the chemical stability tests had no significant effect on KIC (p\u3e0.05). Bioactivity tests revealed that wollastonite GC induced the formation of bone-like carbonated hydroxyapatite when soaked in SBF. Moreover, wollastonite GC supported osteoblast attachment and proliferation. Osteoblast spreading, focal adhesion formation and alkaline phosphatase activity on this GC were comparable to those on a control zirconium-oxide-based ceramic, indicating excellent biocompatibility. In conclusion, wollastonite GC is a promising material for non-metallic dental implant applications based on five tested qualities: mechanical properties, chemical stability, machinability, excellent bioactivity and biocompatibility

Machinability studies of machinable glass-ceramic materials: macor and boron nitride

Machinability assessment of two ceramic materials was carried out using uncoated carbide tool inserts under dry conditions. The materials investigated were Macor and Boron nitride and the machining operation was a continuous operation (turning). The objectives of this investigation were to generate reliable machining data in terms of surface finish, tool life and cutting force in relation to cutting speed, feed rate and depth of cut. The cutting tests were carried out using one-variable-at-a-time and design of experiments. For one variable at-a-time experiment, surface finish, cutting forces and tool life were measured. In these tests the cutting variables i.e, cutting speed, feed rate, depth of cut and nose radius were varied to study their effects on the surface finish, tool life and cutting forces. With the design of experiments, the combined effects of the cutting variables were investigated on the machining responses. The experimental data on the design of experiments were analysed by the response surface methodology. Using the mathematical models for different responses, a computerized machinability data base system was developed to facilitate the optimum selection of cutting parameters

Study On the Development of the Alumina - Rare Earth Phosphate Machinable Composites for Biomedical Applications

Alumina, being a ceramic material, is very hard and strong, is a well-known bioinert ceramics, useful for many implant applications. But strong atomic bonding results in poor machinability in alumina, which is a useful and required property for implants as the shape and dimensional accuracy & criticality are very strict. Hence being a poorly machinable material wide applicability of alumina as implant material is restricted. In the present work, two different grades (C and R) of commercial grade high pure alumina is studied for its machinability (drilling character) by incorporating a weak interphase material, rare earth phosphates (REP`s), namely lanthanum phosphate (LaPO4) and yttrium phosphate (YPO4). Variation of REP was studied between 10 – 50wt. % for both the aluminas. Both the phosphates were stable and found to remain inert (no reaction with alumina) on sintering upto 1600oC, making a true composite character of the alumina-REP sintered compositions. Microstructural studies showed well distributed alumina and rare earth phosphates grains after sintering. All the sintered samples were found to be drillable for all the condition. Only a threshold value of REP content was observed at 1600oC for the higher reactive alumina. Biological studies showed positive results for all the compositions studied. CAl2O3 with 30wt. % REP content sintered at 1600oC was found to be machinable with a densification of >85% and strength >150MPa

Automated Rapid Manufacturing Feedback for Design Considering Advanced Joining Processes

As manufacturing advancements continue to develop, designers must be able to consider these technologies during the design process. Unfortunately, many of these new technologies, such as additive and advanced joining, have many nuances that require expert knowledge to effectively apply. Additionally, new design techniques, such as topology optimization, allow users to create geometries that are traditionally not manufacturable. The approach presented in this thesis bridges the gap of expert knowledge between component design and a new advanced manufacturing technique, specifically linear friction welding to form monolithic components from multiple individual raw material blanks. The first step of the approach analyzes a part geometry to determine the unmachinable regions. This is done by converting an input tessellated shape into a voxelized solid and analyzing different axial cutting tool approach directions that could occur during a milling operation. Areas that the tool cannot access remain, which indicate regions of unmachinable solids. These solids are then used to determine areas where pre-joining machining could occur, taking advantage of the capabilities of linear friction welding. This is done using an existing part decomposition method while using a two-objective search optimizing total cost of manufacturing and total unmachinable volume. Decomposition configurations yield new set-ups of individual sub-volumes to determine unmachinable volume remaining and manufacturing plans are created by rebuilding the configurations to determine total cost of manufacturing. Results of the work demonstrate the ability to determine manufacturing plans and the potential tradeoffs of complex geometries, processing, and costs

Automated Tradeoff Analysis of Cost Versus Machinability for Design Feedback

As CAD tools become more sophisticated, engineers are able to more easily create complex part geometries with minimal mass given strength and stiffness requirements. However, these complex part geometries can be difficult to subtractively manufacture, which consequently increases manufacturing cost and production time. This thesis presents a method independent of CAD kernels for use early in the design process to automatically evaluate a given part's machinability and to provide visual geometric additions that decrease manufacturing cost while maintaining the part's strength and stiffness requirements. Slicing a single part into multiple sub-parts, which are joined together after undergoing pre-machining, offers additional possibilities for cost reduction and machinability improvement by utilizing smaller stock material that requires fewer machining operations. The resulting part geometry for each candidate is determined by intersecting the machinable geometries for each individual machine setup, and may have some amount of added volume over the as-designed part. Evaluating and culling candidates based on two objectives (added volume and cost) provides the design engineer with a set of Pareto-optimal solutions that show where material can be added to reduce manufacturing costs. These methods are implemented and tested on five example parts to demonstrate their capability and utility